The invention relates to a steering device for missiles, which are steered onto airplanes by means of a target seeker, wherein the target seeker is continuously directed towards a target, and a sight line rate signal proportional to the rate of change in space of the sight line to this target is applied to a steering controller.
In a prior art steering device of this type (German Pat. No. 1 406 578) the target seeker comprises a gyro rotor, which carries an optical system in the form of a Cassegrain system, the optical axis of which coincides with the axis of rotation of the gyro rotor. A reticle rotating also with the gyro rotor is provided in the image plane of the optical system and has on one half, for example, alternatingly transparent and opaque sectors or a checkerboard pattern and on the other half a system of concentric alternatingly transparent and opaque rings. The radiation passing through the reticle and through a filter transparent to infrared radiation falls on an infraredsensitive detector, which provides a modulated a.c. signal, when a target outside the optical axis has been detected. The phase of the a.c. signal obtained after demodulation depends on the direction of the target deviation from the optical axis of the system, and the amplitude of the a.c. signal depends on the amount of the target deviation. The gyro rotor is diagonally magnetized and is surrounded by an annular coil. The a.c. signal appropriately amplified is applied to this annular coil, whereby torques are applied to the radially magnetized gyro rotor cyclically with the frequency of rotation, and the gyro rotor will precess with the optical axis of the system onto the target. Thereby the gyro rotor is caused to follow the target continuously with its axis of rotation and the axis of the optical system.
In accordance with the gyroscope laws, the signals required therefor in the annular coil are proportional to the angular rate of the sight line in space, the inertial sight line rate. As, with straight and uniform movement of missile and target, a collision course will be steered when the sight line from the missile to the target remains stationary in space, the signals applied to the annular coil are, at the same time, applied to the steering controller of the missile as sight line rate signals, whereby the heading rate of the missile becomes proportional to the inertial sight line rate.
Such missiles are used, for example, as air-to-air missiles, the target being the hot gases of the jet engines of airplanes.
It is also known to detect the deflection of the axis of the gyro rotor with respect to the missile longitudinal axis and to determine the "look angle". With the prior art steering devices the look angle signal is, however, applied to the steering controller as the sole steering command, whereby the look angle is controlled to become zero and the longitudinal axis of the missile is directed to the target. Thereby, however, the missile is guided to the target in less than the most favorable manner.
The misdistance of air-to-air missiles the target seekers of which are equipped with infrared sensitive detectors, in paticular InSb-detectors, can be substantially impaired in the proximity zone of the target. It has been found that this is due to the presence of so-called "hot spots". "Hot spots" are nodal areas within the exhaust gas jet of jet engines of modern fighter planes, which to a particular extent emit radiation within the sensitivity range of InSb-detectors. During afterburner operation the radiation intensity in the "hot spots" may assume such high values that the hot spots are detected by the target seeker and can be pursued as dummy targets. As such hot spots may occur at a distance of up to 15 meters from the tail of the airplane, this means a large misdistance from the target proper even with otherwise faultless steering of the missile.
But even if the pursuit of the target is not disturbed by hot spots, for example with r.f. target seekers, it is generally desirable to steer the missile to a point which is somewhat offset along the airplane longitudinal axis from the nose, for example towards the cockpit, where a hit is normally more efficient.
It is the object of the invention, with a steering device of the type defined in the beginning to steer the missile to a point which is offset from the nose in the direction of the airplane longitudinal axis relative to the point pursued by the target seeker.
According to the invention this object is achieved in that a sensor responding to the "look angle" between missile longitudinal axis and optical axis of the seeker is provided, and the look angle signal from this sensor is applied to a threshold switch, which provides an output signal of corresponding sign, when a positive threshold value is exceeded or a negative threshold value is fallen below; that an approach sensor is provided, which provides a distance signal in accordance with the distance between missile and airplane, and that the output signal from the threshold switch and the distance signal are applied to a combining circuit for forming a lead signal applied to the steering controller, said lead signal deflecting the trajectory of the missile towards a point offset in the direction of the airplane velocity vector with respect to the target, to which the target seeker is directed, when the distances are small and the look angles are large.
In the idealized case of straight uniform movement of target and missile, the missile is steered so as to keep the sight line to the target stationary in space. The larger the angle becomes between the missile longitudinal axis and the sight line, the larger will be the angle between sight line and airplane velocity vector. When the velocity vector of the target airplane extends in the direction of the sight line, the missile has to fly in the direction of the sight line and its longitudinal axis is aligned therewith and thus also with the axis of the target seeker. The "look angle" is then zero. If, however, the airplane moves at an angle transversely to the sight line, the missile longitudinal axis has to form such an angle with the sight line that it, and thereby also the direction of movement of the missile, are directed to a point which is in front of the airplane in the direction of movement thereof. A lead signal will be generated only, if the angle between sight line and flight velocity vector and thus the look angle exceed a certain predetermined level. The sign of the lead signal is determined by the sign of the look angle.
Furthermore, the lead signal is dependent on the distance between missile and target airplane. At a large distance of the missile from the target airplane, no or practically no lead signal is required, because, as viewed from large distance, the angular rate of the sight line vector to the target airplane and, for example, that of the sight line vector to a "hot spot" are practically identical. A lead signal becomes effective at small distances from the target.
Two embodiments of the invention are described in greater detail hereinbelow with reference to the accompanying drawings.